gistfile1.txt

SQL the langauge we use to get information out of normalized date structures   

Select clause tells you which 
From clause tells you which
Where clause dictates which row you get back out

Answer.where(question_id=3).map &:response
Select *  = select all    is equivalent to .select(:response), but with the last one use and id otherwise you get back all the items, even if there are millions


Find all authors with an email of Shakespeare.email.com
SELECT *
FROM authors
WHERE email = "Shakespeare.email.com"
IN RAILS:  Author.where(email:"shakespeare.email.com")

Find 3 most recent answer
SELECT *
FROM answers
ORDER BY created_at DESC
LIMIT 3;
IN RAILS: Answer.order(created_at: :desc).limit(3)

Find author who was created most recently
SELECT *
FROM authors
ORDER BY created_at DESC;
LIMIT 1
IN RAILS:  

11:20...Find the number of answers for each question_id(group):  You can't select something you're not grouping by.  You can put aliases in fields.
SELECT count(id) AS number_of_answers    (when you use count, it doesn't matter what is in parens)
FROM  answers AS a
GROUP BY question_id
IN RAILS: Answer.group(:question_id).select("count(id) AS number_of_answers").first

Find the last time  question of each type was created(group)
SELECT max(created_at), question_type
FROM questions
GROUP BY question_type

Find the number (count) of each type of question in the database
SELECT count(id) AS question_tyoe
FROM  questions
GROUP question_type
IN RAILS: question.group(:question_type).select("count(id) AS num, question_type")

the more you can cosolidate things down into a singular database call, the fatser it will run
read about JOIN clause

indices

making records in seeds  12:07
to add indices 12:09
ALWAYS PUT INDICES ON THE FOREIGN KEYS, then use your judgement about how users use the system to put foreign keys on other things.